Engine valve means and porting

ABSTRACT

1. AN IGNITION TIMING CONTROL SYSTEM COMPRISING, IN COMBINATION AN AUTOMOTIVE VEHICLE INTERNAL COMBUSTION ENGINE HAVING AN INTAKE SYSTEM INCLUDING A CARBURETOR FOR MIXING FUEL WITH INTAKE AIR TO PRODUCE A COMBUSTIBLE MIXTURE, AND IGNITION PLUGS TO IGNITE SAID COMBUSTIBLE MIXTURE, AN IGNITION DISTRIBUTOR FOR SUPPLYING HIGH VOLTAGE CURRENT TO SAID IGNITION PLUGS OF SAID ENGINE IN ACCORDANCE WITH A PREDETERMINED SEQUENCE, A VACUUM ADVANCE DEVICE RESPONSIVE TO ENGINE INTAKE VACUUM PRODUCED IN SAID INTAKE SYSTEM DOWNSTREAM OF SAID CARBURETOR FOR ADVANCING THE IGNITION TIMING OF SAID IGNITION DISTRIBUTOR, AND VALVE MEANS CONNECTED IN COMMIUNICATION WITH SAID ENGINE INTAKE SYSTEM BOTH UPSTREAM AND DOWNSTREAM OF SAID CARBURETOR AND WITH SAID VACUUM ADVANCE DEVICE, SAID VALVE MEANS BEING ARRANGED TO CONTROL A VACUUM TO BE INTRODUCED INTO SAID VACUUM ADVANCE DEVICE IN ACCORDANCE WITH THE OPERATING MODES OF SAID ENGINE IN TERMS OF AN ABSOLUTE LEVEL IS INTRODUCED INTO SAID THE VACUUM AT THE ABSOLUTE LEVEL IS INTRODUCED INTO SAID VACUUM ADVANCE DEVICE DURING ACCELERATION OF SAID VEHICLE TO EFFECT A VACUUM ADVANCE IN SAID IGNITION DISTRIBUTOR AND SUCH THAT THE VACUUM AT SUCH AN ABSOLUTE LEVEL IS AT LEAST PARTIALLY REDUCED AND INTRODUCED INTO SAID VACUUM ADVANCE DEVICE DURING CRUISING OPERATION OF SAID VEHICLE AND DURING DECELERATION THEREOF TO EFFECT A DESIRED REDUCTION IN THE VACUUM ADVANCE.

United States Patent [:91

Kobayashi, et al.

[ Sept. 16, 1975 IGNITION TIMING CONTROL SYSTEM Inventors: NohuyukiKobayashi; Masahiko Nakada; Masanori Hanaoka, all of Aichi-ken, Japan[73] Assignee: Toyota Jidosha Kogyo Kahushiki Kaisha, Aichi-ken, Japan[22] Filed: Jan. 3,1974

[2]] Appl. No.: 430,402

Primary Examiner- Charles M yhre Assistant Examiner-Tony Argenbright Attorney- Toren, McGeady and Stanger [57] ABSTRACT and an exhaust gasrecirculation system. The ignition timing control system comprises valvemeans in communication with the engine intake system upstream anddownstream of the carburetor and with the vacuum advance device forcontrolling a vacuum, to be introduced into the latter, in accordancewith the engine operating modes in terms of an absolute level of theintake vacuum. During acceleration of the automobile, the vacuum at theabsolute level is introduced into the vacuum advance device to effectsuch a vacuum advance in the ignition distributor as to allow theexhaust gas recirculation system to minimize the nitrogen oxide contentin the engine exhaust gases while minimizing adverse effects upon theoperating characteristics of the automobile. During cruising operationof the automobile and when it is being decelerated, the vacuum at suchan absolute level is at least partially reduced and introduced into thevacuum advance device to effect a reduction in the vacuum advance suchas to allow the exhaust gas recirculation system to minimize thenitrogen content while again minimizing adverse effects upon drivingcharacteristics. In the valve means, temperature responsive means isprovided, which is reponsive to the warm-up condition of the engine forrestricting operation of a valve mechanism of the valve means such thatthe valve mechanism is forced to introduce therethrough the intakevacuum into the vacuum advance device, until engine warm-up is attained,and such that the valve mechanism is released from the forcedintroducing action to restore its normal condition depending upon theabsolute level of the intake vacuum, after the engine warm-up conditionis An ignition timing control system is provided for use attained. withan automotive internal combustion engine having a carburetor, adistributor, a vacuum advance device 5 Claims,2 Drawing Figures I x i 1LI [1 [I I] I 1 l .I

I L 0' A, 32 3| Mmngwsw 1 5 ms 3.905342 SHEET 1 0f 2 FIG. Ia FIG 2 w d ENOx c 5 HC g e a 02 E if, a L b g 2 INTAKE MANIFOLD VACUUM FIG. lb

NOx

(ADVANCE) Y (RETARD) IGNITION mama FIG. 3 39 4O '2 2? PATFMTWSE P3.905.342

slain 2 BF 2 FIG. 4

IGNITION TIMING CONTROL SYSTEM BACKGROUND OF THE INVENTION The presentinvention relates to ignition timing control systems for automotiveinternal combustion engines, and. more particularly, to an improvedignition timing control system, by which the ignition timing iscontrolled to minimize nitrogen oxide content in the engine exhaustgases without adversely affecting the operating characteristics of theautomobile when used with an exhaust gas recirculation system.

Some retardation in ignition timing has been found remarkably effectivein reducing the noxious content in engine exhaust gases of automotiveinternal combustion engines. Such retardation will cause, on one hand,substantial increase in the engine exhaust gas temperature, which inturn will lead to reduction in the unburned content of elements such ashydrocarbons (I-IC). Retardation will also cause substantial decrease inthe combustion temperature, which will likewise lead to reduction in therecombined content of elements such as nitrogen oxides (NO In oneconventional ignition timing control system utilizing the aboveprinciple, a differential between intake manifold vacuum and atmosphericpressure is employed to control a vacuum advance device which isoperative to advance ignition timings of an ignition distributor.

On the other hand, dilution of the combustible mixture with a portion ofthe engine exhaust gases has also been found to decrease the combustiontemperature and accordingly effective in reducing the NO, content. Thus,an exhaust gas recirculation system has been proposed, by which aportion of the engine exhaust gases are recirculated between the intakesystem and the exhaust system in accordance with the engine operatingmodes.

Ignition timing control devices and exhaust gas recirculation systemshave been found so critical in their ignition retarding and mixturediluting operations, that they will necessarily invite decrease in theengine output and/or deterioration in the operating characteristics ofthe automobile. Thus, prior art techniques have not succeeded in solvingthe problem of reducing the noxious content, especially the N emissionfor all the running conditions of the automobile.

It is therefore an object of the present invention to provide animproved ignition timing control system .for use with an automotiveinternal combustion engine with a view to eliminating the abovedrawbacks.

Another object of the present invention is to provide an improvedignition timing control system of the above type, by which the ignitiontiming is controlled as to minimize the NO, content in the engineexhaust gases without adversely affecting the operating characteristicsof the automobile when used with an exhaust gas recirculation system.

SUMMARY OF THE INVENTION Briefly, the present invention may be describedas an ignition timing control system for an automotive vehicle internalcombustion engine having an intake system including a carburetor formixing fuel with intake air to produce a combustible mixture, anignition distributor supplying high tension current to the ignitionplugs of the engine in accordance with a predetermined sequence, avacuum advance device responsive to engine intake vacuum produced insaid intake system downstream of said carburetor for advancing theignition timing of said ignition distributor, and an exhaust gasrecirculation system in communication with both said intake system andthe exhaust system of the internal combustion engine for recirculatingtherebetween a portion of the exhaust gases in accordance with engineoperating modes whereby the nitrogen oxide content of the exhaust gasesis reduced. The invention is particularly characterized by theimprovement which comprises valve means connected in communicationbetween the intake system and the vacuum advance device to apply to saidvacuum advance device a vacuum which controls operation thereof inaccordance with the operating condition of the engine. The valve meansare connected to the intake system at points both upstream anddownstream of the carburetor. Retention means in the valve means operateto sense the engine operating temperature and to retain the valve meansin a condition wherein only the vacuum pressure from the connected pointdownstream of the carburetor is applied to the vacuum advance deviceuntil the temperature of the engine reaches a predetermined level wherean engine warmed-up condition is achieved. Subsequently, control meansresponsive to the vacuum pressure existing at the connected pointdownstream of the carburetor control operation of the valve means toapply to the vacuum advance device a control vacuum which selectivelycombines the vacuum pressure derived from the point downstream of thecarburetor with atmospheric pressure derived from the point upstream ofthe carburetor to balance the timing advance in accordance with thepressure sensed at the connected point downstream of the carburetor. Inthis manner, the invention operates to cause the exhaust gasrecirculation system to minimize the nitrogen oxide content of theexhaust gases while also minimizing the adverse effects produced uponthe driving characteristics of the automobile.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of thepresent invention will be apparent from the following detaileddescription of the preferred embodiments thereof taken in conjunctionwith the accompanying drawings, in which:

FIGS. 1(a) and 1(b) are graphical presentations of 'the noxious contentof the engine exhaust gases taken Referring first to FIG. 1(a), in whichthe N01 emission presence in the exhaust gas recirculation isrepresented against the ignition timing, when the engine is operating inthe cruising range, using the amount of recirculation as a parameter,the BC emission as well as the automotive operating characteristics areshown taken against the ignition timing. In cases where the amount ofrecirculation is percent, percent and percent, the NO, emission is seento decrease with increase in the ignition retardation, as shown bycurves a a and a respectively. For all recirculation conditions, on theother hand, it is also found that vehicle driving characteristics becomedeteriorated when the ignition retardation exceeds a level illustratedby a characteristic curve b. More specifically, the automobile startsvibrations at a level of the ignition retardation representedlongitudinally of the characteristic curve b. In view of the curves a aand a and b, it can be deduced that the minimum amount of NO, emissionpresence in the exhaust gas recirculation is represented by a value a inthe range of ignition timing of acceptable operating characteristics,namely, in the lefthand side of the curve b. and that this minimumamount a is obtainable even when the ignition retardation is augmentedto as large a value as a value x. As shown by a curve c, on the otherhand, the HC emission is decreased uniformly with increase in theignition retardation. Thus, with a view toward reducing the HC emission,it is preferable to retard the ignition timing as much as possible. Inorder to be compatible with the reduction in the NO, emission resultingfrom the exhaust gas recirculation, however, it can be deduced thatsetting the ignition timing at the level x will satisfy requirements toa satisfactory extent during cruising operation of the automobile.

Turning now to FIG. 1(b), the NO, emission presence in the exhaustemission is also plotted against the ignition timing, when the vehicleis accelerating, using the amount of recirculation as a parameter. Asseen from curves at to a corresponding, respectively, to the cases wherethe amount of recirculation is 0 percent, 3 percent, 6 percent and 9percent, the NO r emission will also be decreased with increase in theignition retardation, with the concurrent abrupt decrease in engineoutput torque.

Thus, engine output torque may be used as a parameter so as to representthe NO, emission against the ignition timing. Curves d, and d areintended to represent relationships between the NO emission and theignition timing, respectively, in the cases where the output torquesduring acceleration have the values of IO Kg-m, 9 Kg'm and 8 Kg-m. Thevalue at which the minimum NO,r emission is obtained for the differentoutput torques is seen to fall at a point y. which is shifted from thevalue x to an advance side of the ignition timing. In other words, theminimum N0 emission for the same output torque can be obtained at themore advanced point y during the accelerating condition of theautomobile. It has also been experimentally revealed that a conventional ignition vacuum advance device can, if properly adjusted,effect ignition advance to the value y whereas without the vacuumadvance device the obtainable ignition timing would be located at thevalue x or at a slightly retarded value than the value x.

In summary, it may be said that in order to obtain the minimum NO,emission presence in the exhaust recirculation without adverselyaffecting vehicle operating characteristics, the ignition timing shouldbe vacuum-advanced during acceleration,but the vacuum advance of theignition timing should be terminated for cruising operation or it shouldbe limited to such a degree determined by taking into consideration thedeterioration of the vehicle operating characteristics.

An improved ignition timing control system according to the aboveconcept will now be described in conjunction with FIGS. 3 and 4 to 6.Referring first to FIG. 3, a carburetor I having a customary venturi 2,are both mounted in an intake system of an automotive internalcombustion engine formed with an atmospheric pressure outlet 3 upstreamof the venturi 2 and with an intake vacuum outlet 5 downstream of athrottle valve 4. These two outlets 3 and 5 are connected to achange-over valve 20 according to the present invention by way of airconduits 6 and 7, respectively. This change-over valve 20 is in turnconnected to a vacuum advance device 10 of a distributor 9 by way of anair conduit 8. With these connection arrangements, the change-over valve20 can introduce selectively atmospheric pressure, the intake manifoldpressure or an intermediate pressure into the vacuum advance device 10in accordance with the engine operating modes in terms of an absolutelevel of the intake vacuum, as will be hereinafter detailed.

The change-over valve 20 is formed with inlets 21 and 22, which areconnected to the air conduits 6 and 7, respectively, and with an outlet23 which is connected to the air conduit 8. In the change-over valve 20,two coextensive chambers 24 and 25 are formed, which are incommunication with the two inlets 21 and 22, respectively. Between thechambers 24 and 25 there is formed a passage 26 which in turn is incommunication with the outlet 23. The change-over valve 20 maypreferably be arranged in an upright manner, as shown. Above the chamber24, there is formed a passage 27, through which a working medium, forexample, engine cooling water, engine lubricating oil or hot air for achoking operation can pass in order to provide therein a temperaturemedium representative of temperature variations in engine operatingconditions. A shaft 28 is vertically movably inserted in chambers 24 and25, passing through passages 26 and 27. In the chamber 25, shaft 28 isconnected by means of a fastening member 29 to a diaphragm member 31, onthe back of which a spring 30 is mounted for biasing the shaft 28 in thedownward direction. At the opposite side of the chamber 25, thediaphragm 31 forms an atmospheric chamber 33 which is vented to theatmosphere through an air vent 32. The shaft 28 is formed with a vacuumvalve member 34 between the chamber 25 and the passage 26 so as toprovide and block communication therebetween. The shaft 28 is alsoformed with a stopper 35 between the chamber 24 and the passage 26. Thisstopper 35 is arranged such that it can contact with the lower surfaceof an atmospheric valve member 37, on the back of which a spring 36 ismounted for biasing the valve 37 in the downward direction and and whichis operable to provide and block communication between the chamber 24and the passage 26. It should be noted here that the two valve members34 and 37 have synchronized relative positions such that when the formerprovides communication between the chamber 25 and the passage 26 thelatter blocks communication between the chamber 24 and the passage 26,and vice versa.

The shaft 28 has its upper extending end 28 movable into and out of thepassage 27 which is sealed off from the chamber 24 by means ofa sealingmember 38. In this passage 27 is mounted a temperature responsive body39 which is expandable and contractable in accordance with the ambienttemperature. To this temperature responsive body 39 is connected a cam40 which is slidably accommodated in the passage 27. This cam 40 has acut-away portion 40' at such a position as to face the extending end 28'of the shaft 28. Before warm-up of the engine is completed, the workingmedium, e.g., the engine cooling water, is at a relatively lowtemperature, so that the temperature responsive body 39 is in acontracted condition with the result that the cam 40 is pulled in thelefthand direction to place its wider portion over the extending end 28'of the shaft 28. Thus the extending end 28' is prevented from movinginto the passage 27, so that the shaft 28 can be said to assume a firstposition in which it cannot move upwardly. After the engine warm-upcondition is attained, the temperature responsive body 39 is expandedsufficiently to move the cam 40 rightwardly. Then, the extending end 28of the shaft 28 faces the cut-away portion 40 of the cam 40, so that theshaft 28 is released from the retaining action of the wider portion ofthe cam 40 to enable its upward movement into the passage 27. In thisinstance, the shaft 28 can be said to assume a second position.

Thus, when the engine is being warmed up, the shaft 28 is restricted bythe cam 40 from upward movement and is held at the first position. Thevalve member 34 allows communication between the chamber 25 and thepassage 26, but the valve member 37 is spaced from the stopper 35 toshut off communication between the chamber 24 and the passage 26. As aresult, only the intake vacuum from the carburetor l is introduced intothe vacuum advance device via the air conduit 8 to thereby carry out aproper amount of vacuum advance in the dir ributor 9.

After the engine warm-up has been completed, the movement of the cam 40will release the shaft 28 which will thus be capable of moving upwardly.During the accelerating phase of engine operation, the large effectivearea of the throttle valve 4 will establish a relatively smaller, i.e.,a more positive relative pressure, so that the vacuum in the chamber 25exerted on the diaphragm 31 is not so sufficient to enable the diaphragm31 to flex upwardly against the biasing action of the spring 30.However, the shaft 28 cannot hold at the first position to provide thesame degree of communication between the chamber 25 and the passage 26around the valve member 34, thus permitting introduction of the intakevacuum into the vacuum advance device 10 to a somewhat lesser degree.Thus, a slight but proper amount of vacuum advance is effected in thedistributor 9.

When, on the other hand, the automobile is running in the cruisingcondition or in the decelerating condition, an intake vacuum ofconsiderably large level is built up in the intake system downstream ofthe carburetor, that is, a relatively more negative pressure isdeveloped. Then, the diaphragm 31 is flexed upwardly by the pressuredifferential between the atmospheric pressure in the chamber 33 and thegreater intake vacuum introduced into the chamber 25. As a result, theshaft 28 is also lifted to have the valve member 34 block communicationbetween the chamber 25 and the passage 26, whereas the chamber 24restores communication with the passage 26 with the aid of the valvemember 37 which is brought into contact with the stopper 35. As aresult. the atmospheric pressure in the intake system upstream of thecarburetor 1 is introduced into the vacuum advance device 10, so thatthe distributor 9 is free from any vacuum advancement.

Reverting to FIG. 2, the vacuum advance angle during the engine warm-upis shown at a curve e, which is plotted against the intake vacuum. Thiscurve e will be self-explanatory from the discussion set forthhereinabove.

In FIGS. 4, 5 and 6, other embodiments of the changeover valve 20 areshown, in which like reference numerals will indicate like elements orcounterparts of the embodiment as shown in FIG. 3.

The difference of the embodiment of FIG. 4 from that of FIG. 3 residesin that a bypass conduit 42 having an orifice 41 is interposed betweenthe chamber 25 and the passage 26, and in that an additional passage 24'having an orifice 43 is provided which extends from the inlet 21 to thechamber 24. With these constructional differences, therefore, the intakevacuum will pass, during acceleration of the automobile, not onlythrough the passage 26 but also through the bypass passage 42, and willbe introduced into the vacuum advance device 10. Conversely, duringcruising operation, the vacuum in the chamber 25 is supplied to thevacuum advance device 10 via the bypass passage 42 even in the absenceof communication between the chamber 25 and the passage 26 due to theblocking action of the valve member 34. Thus, the absolute level of thevacuum to be introduced into the vacuum advance device 10 under thelatter condition is reduced to an intermediate value between those ofthe intake vacuum and the atmospheric pressure. As a result, thedistributor 9 can be vacuum-advanced to some extent, in the case whereconsiderable intake vacuum is developed, as illustrated by the brokenlinefin FIG. 2. In this instance, it should be appreciated that theorifice 41 serves to prevent excessive reduction of the vacuumestablished in the chamber 25 whereas the orifice 43 serves to preventexcessive reduction of the vacuum in the passage 26.

The embodiment of FIG. 5 is slightly modified from that of FIG. 4, suchthat the valve member 34 for providing and blocking communicationbetween the chamber 25 and the passage 26 is eliminated and replaced bya sealing member 44, which serves to block the communicationtherebetween at all times. since the former is always in communicationwith the outlet 23 via the bypass passage 42. Other con structionalarrangements and operational features are quite similar to those of theembodiment of FIG. 4, and as such repeated explanation thereof will beomitted.

In the embodiment of FIG. 6, a diaphragm member 46 is interposed betweenthe chambers 24 and 25, and a spring 45 is mounted on the back of thediaphragm member 46 for imparting a biasing spring action thereto in theupward direction. A passage 47 is provided which is in communicationwith the chamber 25 by way of the bypass passage 42. This passage 47 isformed with an orifice 48, through which it is in communication with theupper portion of the chamber 24 only. Between the chamber 24 and thepassage 47 there is interposed a valve member 49 which is operative toestablish and cut off communication therebetween. A spring 51 isinterposed between this valve member 49 and a fastening member 56, whichis operative to connect the diaphragm member 46 with a shaft 50, forapplying an upward biasing force to the valve member 49. This shaft 50is formed with a stopper 52 which can contact the valve member 49. Theshaft 50 is further formed with an engagement member 54 which ispositioned in a passage 53. in this passage 53 is mounted a cam 55 whichis connected to the temperature responsive body 39. This cam 55 isformed with a stepped portion 55' which is engageable with theengagement member 54.

With this arrangement, before engine warm-up has been completed, theengagement member 54 is pulled leftward by the temperature responsivebody 39, so that it is brought into engagement with the stepped portion55 of the cam 55. As a result, the shaft 50 is restricted from movingdownwardly, that is, just opposite to the direction of the previousembodiments. At this stage, the valve member 49 continues blockingcommunication between the chamber 24 and the passage 47, so that thevacuum prevailing in the chamber 25 will be introduced into the vacuumadvance device via the bypass passage 42.

After engine warm-up has been completed, the engagement member 54 isdisengaged from the stepped portion 55 to make it possible for the shaft50 to move downwardly. When, in this situation, the automobile isexperiencing an accelerating operation, then the intake vacuum has notachieved so sufficiently large a level as to flex the diaphragm member46. Therefore, the shaft 50 is held at the upper position, so that theintake vacuum is also introduced into the vacuum advance device 10.When, on the contrary, the automobile is in the cruising condition or inthe decelerating condition, then the sufficiently developed intakevacuum will flex the diaphragm member downwardly against the biasingaction of the spring 45 to thereby lower the shaft 50. Thus, its stopper52 is brought into contact with the valve member 49 to form a passagewaytherearound between the chamber 24 and the passage 47. As a result, theatmospheric pressure in the chamber 24 is introduced into the vacuumadvance device 10 in addition to the intake vacuum via the bypasspassage 42. In like manner as in the embodiments of FIGS. 4 and S, theabsolute level of the vacuum to be supplied to the vacuum advance device10 is reduced to have an intermediate value between the intake vacuumand the atmospheric pressure. A vacuum advance of some degree is,therefore, effected in this embodiment. Here, the orifices 41 and 48 arealso operative to prevent excessive reduction in the vacuum in thechamber and in the atmospheric pressure in the carburetor 1.

As is apparent from the foregoing description, before the engine warm-uphas been completed. the engine is vacuum-advanced according to thescheme of the present invention irrespective of the absolute level ofthe intake vacuum. The instability in the automotive operatingcharacteristics under this condition can be prevented from being furtherdeteriorated or adversely affected. By making the best use of the intakevacuum which varies in dependence upon the running condition of theautomobile, the engine is vacuum-advanced in the accelerating conditionto properly advance the ignition timings. 1n the cruising condition, onthe contrary, the engine is not vacuumadvanced or at most slightlyvacuum-advanced, so that the ignition timings are retarded from a valuewhich might otherwise be attained by the vacuum advance device. itshould, therefore, be appreciated as an advantage of the presentinvention that the N0 emission presence in the exhaust gas recirculationcan be minimized for all the running conditions to such an extent as tobe free from adverse effects upon vehicle operating characteristics, or,in other words, that efficiency in cleansing the engine exhaust gases isconsiderably improved with the possible deterioration in the operativecharacteristics due to the cleansing operation being maintained at aminimum level. it should also be appreciated that the ignition timingretardation during the cruising operation will lead not only to materialreduction in the NO emission due to the exhaust gas recirculation, ashas been discussed, but also to additional reduction in the NO, emissiondue to decrease in the combustion temperature and also to reduction inthe HC emission due to increase in temperature in the engine exhaustgases. in the decelerating mode of engine operations, moreover. theabrupt increase in the absolute level of the intake vacuum willterminate the vacuum advance in accordance with the present invention.Therefore, it should also be appreciated that the present invention isalso applicable during engine deceleration such that the reduction inthe driving torque will strengthen the obtainable braking action on theengine.

Moreover, the embodiments of FIGS. 4 to 6 are considered superior tothat of FIG. 3 in that they can provide better operating characteristicsin cruising operation because vacuum advance of some degree is effectedeven in that phase of operation. The embodiment of FIG. 5 is consideredsuperior to that of FIG. 4 in that its construction and operation can bemore simplified because in the former the two valve members 34 and 37need not be synchronized. The embodiment of FIG. 6 can be simplifiedstill further than that of FlG. 5, since the single valve member 49 canperform the required change-over action.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. An ignition timing control system comprising, in combination anautomotive vehicle internal combustion engine having an intake systemincluding a carburetor for mixing fuel with intake air to produce acombustible mixture and ignition plugs to ignite said combustiblemixture, an ignition distributor for supplying high voltage current tosaid ignition plugs of said engine in accordance with a predeterminedsequence, a vacuum advance device responsive to engine intake vacuumproduced in said intake system downstream of said carburetor foradvancing the ignition timing of said ignition distributor, and valvemeans connected in communication with said engine intake system bothupstream and downstream of said carburetor and with said vacuum advancedevice, said valve means being arranged to control a vacuum to beintroduced into said vacuum advance device in accordance with theoperating modes of said engine in terms of an absolute level of saidintake vacuum such that the vacuum at the absolute level is introducedinto said vacuum advance device during acceleration of said vehicle toeffect a vacuum advance in said ignition distributor and such that thevacuum at such an absolute level is at least partially reduced andintroduced into said vacuum advance device during cruising operation ofsaid vehicle and during deceleration thereof to effect a desiredreduction in the vacuum advance.

2. A system according to claim 1 wherein said valve means includes avalve mechanism movable between a first and a second position, saidvalve mechanism operating to apply said intake vacuum into said vacuumadvance device when in its first position and to introduce atmosphericpressure prevailing in said intake system upstream of said carburetorinto said vacuum advance device when in said second position, adiaphragm member responsive to said intake vacuum for moving said valvemechanism into 10 warm-up condition of said engine for holding saidvalve mechanism at said second position irrespective of the operation ofsaid vehicle until warm-up of said engine is attained, and for allowingsaid valve mechanism to move in response to operation of said vehicleafter engine warm-up has been attained, and a bypass passage providingcommunication between said intake system downstream of said carburetorand said vacuum advance device for introducing therethrough intakevacuum into said vacuum advance device such 0 that the absolute level ofthe vacuum to be introduced said first position during acceleration ofsaid vehicle and for moving said valve mechanism into said secondposition during cruising operation of said vehicle and when said vehicleis being decelerated, and temperature responsive means responsive to thewarmed-up condition of said engine for holding said valve mechanism atsaid first position irrespective of the operation of said vehicle untilsaid engine has achieved a warmed-up condition and for allowing saidvalve mechanism to operate in response to movement of i said diaphragmmember after said engine has attained a warmed-up condition.

3. A system according to claim 2 wherein said valve means furtherincludes a bypass passage providing communication between said airintake system downstream of said carburetor and said vacuum advancedevice for introducing therethrough the intake vacuum into said vacuumadvance device, such that the absolute level of the vacuum introducedinto said vacuum advance device during deceleration or cruisingoperation of said vehicle may be reduced to an intermediate levelbetween said intake vacuum and atmospheric pressure.

4. A system according to claim 1 wherein said valve means includes avalve mechanism movable between a first and a second position, saidvalve mechanism when in said first position being operative to effectintroduction into said vacuum advance device into said vacuum advancedevice during deceleration and during cruising operation may be reducedto an intermediate level between the level of the intake vacuum and ofatmospheric pressure.

5. An ignition timing control system comprising, in combination anautomotive vehicle internal combustion engine having an intake systemincluding a carburetor for mixing fuel with intake air to produce acombustible mixture, an ignition distributor for supplying ignitioncurrent to said engine in a predetermined sequence, a vacuum advancedevice responsive to vacuum pressure for controlling the ignition timingof said ignition distributor, valve means connected in communicationbetween said intake system and said vacuum advance device to apply tosaid vacuum advance device a vacuum controlling operation thereof inaccordance with the operating condition of said engine, said valve means40 being connected to said intake system at points both carburetor forcontrolling operation of said valve means to apply to said vacuumadvance device a control vacuum which selectively combines the vacuumpressure derived from said connected point downstream of said carburetorwith atmospheric pressure derived from said connected point upstream ofsaid carburetor to effect a desired vacuum advance in said ignitiondistributor.

